Some aircraft surfaces require to be protected from the accumulation of ice caused by the collection and freezing of ambient moisture. Ice protection is frequently achieved by heating the aircraft skin so that the water catch on the skin is prevented from freezing and is partially or completely evaporated. If the water is not completely evaporated it will run back along the aircraft skin surface and may then freeze and accumulate on a part of the surface that is not heated. There is a danger that the ice so formed will adversely affect the aircraft's efficiency and handling qualities. In addition, any accumulated ice on the aircraft surface may become detached and impact upon another part of the aircraft thereby causing damage. It is particularly desirable to prevent the entry of large pieces of ice into the engine intake, and consequently engine intake ice protection systems usually provide for a complete removal of the water catch by providing sufficient heat to ensure full evaporation of the water.
In UK patent application number GB 2259679 an ice protection system is disclosed for preventing the accumulation of ice on the leading edge of an aircraft engine nacelle nose cowl. The nose cowl comprises a forward compartment formed by a forward bulkhead and a skin structure extending forwardly of the forward bulkhead to form the leading-edge profile. The outer surface of this leading-edge profile is required to be protected from the accumulation of ice thereon. The nose cowl includes a rear compartment between the forward bulkhead and a rear bulkhead, supply duct means extending through the rear compartment and into the forward compartment for the delivery thereto of pressurised hot gases for distribution over the inner surface of the skin structure to prevent accumulation of ice on or to remove ice from the outer surface of this skin structure.
Although the ice protection system described in GB 2259679 has been found to be successful, sufficient heat has to be provided by the pressurised hot gases distributed over the inner surface of the skin structure to produce full evaporation of the film of water passing over the outer surface of the skin structure. The heat required to produce this evaporation is a drain on the fuel consumption of the aircraft, and makes it necessary to use materials such as titanium and stainless steel thereby increasing the weight and cost of the aircraft.
There is therefore a need for an ice protection system which will overcome at least some of the disadvantages associated with the known systems.